A typical conventional phased-array antenna has an arrangement of radiating and/or receiving elements where the relative phase of radio frequency (RF) waves propagated/received through the elements can be controlled to steer the "beam" of the antenna's radiation pattern. In one type of phased-array antenna, known as an active array, each radiating/receiving element has associated electronics that includes at least an amplifier and a variable phase shifter. The distributed nature of the active array architecture offers advantages in, for example, power management, reliability, system performance and signal reception and/or transmission.
One example of a single polarity active array is disclosed in U.S. Pat. No. 5,276,455 (hereinafter "the '455 patent") issued to Fitzsimmons,et al., Jan. 4, 1994, assigned to the same assignee as the present invention and incorporated herein by reference in its entirety. FIG. 7 of the '455 patent, reproduced herein as FIG. 1, is an exploded view of an active array antenna 100 disclosed in the '455 patent for use in receiving or transmitting circularly polarized RF signals. The circularly polarized RF signal may either be fixed left-hand polarized or right-hand polarized.
Antenna 100 has an antenna honeycomb 132, a module honeycomb 128 and a feed honeycomb 134, each having a plurality of waveguides aligned with a corresponding waveguide in the other honeycombs. Each waveguide of honeycomb 132 contains a dielectric 146 and separate polarizer 148. Each waveguide of honeycomb 128 contains an "in-line" active array module 130 (i.e., the substrate of each module 130 is parallel or "in-line" with the direction of the received or transmitted RF signal propagation), and each waveguide of honeycomb 134 contains a dielectric 146.
Further, antenna 100 has a waveguide feed network 112 for propagating RF signals to or from feed honeycomb 134, and multilayer wiring boards 140a and 140b for distributing power and logic signals to modules 130. Multilayer wiring boards 140a and 140b do not propagate the RF signals transmitted or received by antenna 100. Rather, modules 130 perform waveguide-to-waveguide transmission of the received and transmitted RF signals via antenna honeycomb 132 and feed honeycomb 134.
In addition, modules 130 have extension substrates for input and output couplers for inputting and outputting RF signals to or from antenna honeycomb 132 and feed honeycomb 134, as well as a carrier substrate for supporting and interconnecting MMICs for amplifying and phase shifting the received or transmitted RF signals. FIG. 1A shows a cutaway view of the modules 130 showing the embedding of the MMIC phase shifter 180a and the MMIC power amplifier 180b. This type of array can support transmission or reception of a single polarity signal. The polarity of the signal is determined by the physical orientation of the dielectric slab polarizer 146 in the honeycomb 132. The electronic phase shifter in each module allows the beam pattern to be electrically positioned.
As the frequency of the RF signal increases, the element spacing, and thus the size of the phased-array antenna must decrease, in order to not generate grating lobes, at the high scan angles that are required for airborne applications. Accordingly, the size of each receiving element of the phased-array antenna decreases. For many applications, the RF signal has a frequency of well over 10 GHz. As the size of the receiving elements decrease, the space available for the MMICs also decreases. Therefore, it is important to design an MMIC amplifier and phase shifter that will provide the necessary performance while occupying as little space as possible. The length of the electronic module 130 can be increased somewhat, if necessary, to accommodate larger MMIC components. However, this is not desirable since it will cause the array thickness to increase. It is desirable that the antenna be as thin as possible to reduce aerodynamic drag. Further, cutting the aircraft skin so that the antenna may be recessed is impractical because cuts reduce the structural integrity of the aircraft.
Compared to other existing active single polarity phased array antennas, the '455 patent antenna offers improvements in size, thickness, cost, maintainability, reliability, testability, and assembly. But this antenna is still relatively thick for airborne applications and, because of its complexity, is relatively costly.
An example of a lower-cost thinner phased-array antenna that contains an integrated polarizer with a polarity select switching network, is disclosed in co-pending and commonly owned U.S. patent application Ser. No. 08/576,020 by Fitzsimmons, et al., entitled "LOW-COST COMMUNICATION PHASED-ARRAY ANTENNA." The planar configuration of the electronic modules in this antenna allows the antenna to be thinner than other antennas which use in-line modules. This antenna is thin enough to be externally mounted on a commercial aircraft. In addition, it allows each EM signal probe to be connected to its corresponding amplifier without the use of striplines, finlines or slotlines that are used in some conventional phased-array antennas, thereby reducing the complexity of the metallization of the substrate and further reducing signal loss. Furthermore, this planar antenna allows the use of two orthogonal antenna probes, which are required to build an electronically selectable single polarity or dual polarity phased array antenna.
This antenna is shown in FIGS. 2, 2A, 2B, 2C, and 3. This antenna uses planar semiconductor modules 408 that contain orthogonal waveguide probes 502 & 504 that couple the EM signals from the waveguides 406 into the module's low noise amplifiers (LNAs) 508 & 510 inputs. The polarity select network 514 forms a combined RF signal that is electronically selectable between left hand or right hand circularly polarized. Each electronic module then amplifies 520 and phase shifts 524 the circularly polarized signal. This signal is then connected to the stripline combiner networks on the multilayer wiring board 416 which combines the module outputs at the subarray level. The DC power supply filtering and amplifier biasing for each module must be accomplished by the electronics in each module, since this low-cost packaging concept does not allow space on the multilayer wiring board for external components to filter the DC power, to each element. Compared with the '455 patent and other prior art phased array antennas, this antenna is much lower cost, thinner and can provide an electronically switchable dual polarity output.
By using the MMIC electronics circuitry disclosed in FIG. 4 and modifying the packaging concept disclosed in FIG. 2 to include, among other modifications, additional stripline combiner networks in the multilayer wiring board and the associated necessary connections, a dual polarity dual beam phased-array antenna can be constructed. The modules for each element of this antenna contains two MMIC phase shifters, one for each of its two outputs, thereby allowing this antenna to be steered to track two different beams simultaneously.
Another effect of high frequency RF signals is that the MMICs generally cannot be implemented using conventional silicon based technologies. Instead, the MMIC must be implemented using GaAs technology, which is generally capable of operating at very high frequencies. One disadvantage of GaAs components is their high cost. GaAs integrated circuits are typically several times as expensive as conventional silicon integrated circuits. Because of the large number of MMICs in each phased-array antenna, the cost of GaAs can be prohibitive. One approach to mitigating the cost of GaAs MMICs is to shrink the size of the MMICs. The smaller the size of the GaAs MMICs, the less the cost. Also the planar electronics module size is limited by the array element spacing which constrains the area available for MMIC circuitry. Thus, it is doubly important to design MMIC amplifier, phase shifter, switches, phase shift networks, switches and combiner networks that are compact. Another factor that affects MMIC cost is the yield of the circuits to the electrical performance requirements. What is needed is phased array circuit elements and circuit architectures that are small in size, easy to implement and give a high electrical performance yield in GaAs technology. The MMICs in this invention address all of these concerns.